1. Field of the Invention
This invention relates to a method of dicing a semiconductor wafer which suppresses the occurrence of cracks in a chip.
2. Description of the Related Art
A large number of chips are produced by fabricating semiconductor integrated circuits such as ICs, LSIs, etc., on a semiconductor wafer of silicon (Si), etc., by a thin film formation technique, photolithography, impurity implantation technique, and so forth, and then dicing the wafer in both transverse and longitudinal directions along scribe lines of the integrated circuits formed in desired patterns, using a diamond blade rotating at a high speed.
Next, the semiconductor chips after dicing are picked up and aligned on a chip tray by the use of a pick-up collet, the semiconductor chips separated individually are mounted to ceramic substrates or ceramic packages by another pick-up collet disposed separately, and thereafter circuit connections are established by effecting wire bonding to bonding pads that have already been formed into a desired pattern, or by flip chip connection.
After the device formation is completed, the semiconductor wafer is mounted and fixed to an adhesive tape, and is sequentially diced in both transverse and longitudinal directions into chips using a diamond blade as shown in FIG. 2.
Here, the diamond blade is produced by mixing fine particles of diamond in a metal such as nickel (Ni), and is referred to as an "electrodeposition blade" owing to its production process.
In the case of a high quality product, a thin film of titanium (Ti) and gold (Au) is formed on the back of the semiconductor wafer for the necessity of soldering by a eutectic solder. In the case of an ordinary product, the back of the semiconductor wafer is directly bonded to an adhesive tape for the purpose of bonding by an adhesive.
When the width of the scribe line, which has already been formed into a pattern, is about 150 .mu.m, a diamond blade having a tip width of about 80 .mu.m is used, and when the width of the scribe line is 60 to 90 .mu.m, a diamond blade having a tip width of about 25 .mu.m is used. Dicing is carried out to a depth at which the adhesive tape is cut, and when dicing is sequentially repeated along each scribe line in the transverse and longitudinal directions, the chips are separated.
Dicing is generally carried out at a high speed of tens of thousands of revolutions-per-minute (rpm), and a large number of cracks develop on the back of the wafer coming into contact with the adhesive tape because the material of the semiconductor wafer is so hard that the oscillations cannot be absorbed, because the hardness of the semiconductor wafer and that of the adhesive tape are different, and because the occurrence of vibration is unavoidable during the high speed rotation of the diamond blade. In particular, the development of such cracks is notable in so-called tape automated bonding.
Next, after dicing of the wafer is completed, the semiconductor chips are sequentially pushed up from the back of the adhesive tape, are vacuum adsorbed by the pick-up collet and are arranged on the chip tray. During this vacuum adsorption and transfer, a portion of the cracks peels off from the semiconductor chip, scatters to another semiconductor chip, and causes a short-circuit problem during fitting of the semiconductor chip.
In other words, the prior art technology involves the problem that a large number of cracks develop on the separation plane of the semiconductor chips during the dicing process of the semiconductor wafer after the formation of the semiconductor circuit devices, and these cracks scatter and adhere to the plane of other semiconductor chips during a pick-up process.
Japanese Unexamined Patent Publication (Kokai) No. 2-184451 (corresponding to U.S. Pat. No. 4,878,992) discloses two-step dicing in the production of thermal ink-jet print heads. However, the disclosed dicing is for surface chipping and, therefore, the problem of cracks is not caused.